The present invention relates to a pattern transfer method and a transfer apparatus which are usable, for example, for lithography to fabricate semiconductor integrated circuits. More particularly, the present invention relates to a technique whereby a pattern of a mask is transferred onto a radiation-sensitive substrate by using a charged particle beam, e.g. an electron beam, an ion beam, etc.
Methods of transferring a pattern of a mask onto a radiation-sensitive substrate (e.g. a wafer as a substrate of a semiconductor integrated circuit) by using a charged particle beam are disclosed, for example, in Japanese Patent Application Unexamined Publication (KOKAI) Nos. 5-36593 and 5-251317 (the latter corresponding to U.S. Pat. No. 5,260,151). A mask used in these transfer methods has a beam transmitting portion which transmits a charged particle beam and a beam limiting portion which scatters or absorbs the charged particle beam to a greater extent than the beam transmitting portion. The beam transmitting and limiting portions are disposed on the mask according to a pattern to be transferred onto a radiation-sensitive substrate. During transfer process, the whole pattern area of the mask is irradiated with the charged particle beam at a uniform dose. A part of the charged particle beam is scattered or absorbed by the beam limiting portion. Consequently, an intensity contrast is introduced into the charged particle beam which is led to the radiation-sensitive substrate according to the layout of the beam transmitting and limiting portions, thereby enabling the desired pattern to be transferred onto the radiation-sensitive substrate.
In the actual use of the above-described mask, however, the beam limiting portion is caused to generate heat by the energy of the applied charged particle beam. If the beam limiting portion is thermally deformed, the transfer position is displaced, or the transfer pattern is distorted. Thus, the use of the conventional mask is likely to degrade the transfer accuracy.
An object of the present invention is to provide a pattern transfer method and a transfer apparatus which are capable of minimizing the generation of heat from a mask and hence improving the transfer accuracy.